The lumens or channels of medical devices have conventionally been difficult to clean, disinfect, and sterilize. Various methodologies of cleaning flexible endoscopes whether manual or automated rely on flowing a cleaning liquid through the flexible channel and then rinsing the channel. The manual process generally includes performing a step which includes brushing the working channels (suction and biopsy) and only flushing the narrow air and water channels of the endoscope, normally with an enzymatic cleaning solution. The manual cleaning process is variable and depends on the skill of the technician. After manual cleaning the endoscope is transferred to an automated endoscope preprocessor (AER) where it is further cleaned with liquid flow for a brief time and then rinsed with filtered water. A high level of disinfection must be performed before the endoscope is reused.
Several patents such as U.S. Patent no. 20040118437 to N. Nguyen, U.S. Patent no. 20040118413 to Williams et al. and U.S. Pat. No. 6,439,246 to P. Stanley disclose methods of automating cleaning by liquid flow so as to reduce or eliminate manual cleaning steps. Although these methods automate the conventional cleaning process, they still rely on bulk flow of a liquid cleaning composition to accomplish the cleaning step. However, there are inherent limitations in achieving high cleaning levels for strongly adherent contaminants because of the limited viscous shear forces that can be generated at the inner surface of the channel.
To improve the level of cleaning of tubular systems, several patents have disclosed the use of two-phase liquid-gas flow.
U.S. Pat. No. 6,027,572 to Labib et al disclosed a method for removing biofilms and debris from lines and tubing under turbulent flow.
US patent publication 2004/0007255 to Labib et al disclosed the use of two phase flow in which droplets, preformed and entrained in a flowing gas, impact the wall of the channel and fragment and erode contaminants.
U.S. Pat. No. 6,454,871 to Labib et al disclosed a method of cleaning passageways using a mixed phase flow of gas and liquid wherein the flow of gas was sufficient to produce droplets of the liquid which are entrained by the gas and erode or loosen the contaminants when they impact the wall.
U.S. Pat. No. 6,945,257 to Tabani et al. disclosed a method for cleaning hollow tubing and fibers in a hemodialyzer by in situ two-phase flow. The cleaning liquid is introduced into fiber lumens by backflushing to create liquid droplets which are entrained in the gas and erode or loosen contaminants by impact with the wall.
The two-phase cleaning methods discussed above rely on dislodging biofilms or soils by the impact of liquid droplets entrained in a flowing gas at high pressure. However, these methods have intrinsic limitations when applied to the cleaning of long narrow tubes in endoscopes and other medical devices because the pressures required to either generate entrained mist droplet or sufficient droplet impact forces can exceed the maximum pressures for which the devices are rated.
During microscopic examination of liquid-gas flow through narrow hydrophobic channels, we made an unexpected discovery of a new two-phase hydrodynamic cleaning mode that is capable of achieving high levels of cleaning at pressures at or below 35 psi which is suitable for sensitive tubular systems such as endoscopes and similar medical devices. Specifically, we found it possible under certain conditions to flow a liquid cleaning medium and a gas through the internal channel of an endoscope under one or more flow regimes that create surface flow entities in contact with and sliding along the surface of the channel. These surface flow entities have three-phase contact lines and associated menisci which are capable of detaching contaminants with which they come in contact from the internal surface of the channel.
It was unexpectedly found that high levels of cleaning could be produced by these surface flow entities in the absence of entrained liquid droplets provided that the formation of annular liquid films and foam were minimized. The objective of the current invention is the development of a practical cleaning method, apparatus, and cleaning compositions utilizing the above discovery that are especially suitable for the effective cleaning of tubular systems especially endoscopes which have long narrow channels and limited tolerance for high pressure.